This invention relates to testing of integrated circuits, and more particularly to a method for fabricating a probe card apparatus for the testing of integrated circuits.
Integrated circuits (ICs) are formed as multiple, identical, discrete chips on a semiconductor crystal wafer. In wafer form, each of the integrated circuit chips is normally tested by a computer operated apparatus to exercise the circuits and verify the electrical functions, using a testing process commonly referred to as multiprobe testing. Individual chips may be tested similarly in a die carrier test device.
Conventional multiprobe testing apparatus includes a plurality of rigid or flexible probes to connect the IC device to a substrate having fan out wiring to the test equipment. The substrate, typically a probe card, includes a plurality of electrical leads terminating in conductive needles, which in turn make electrical contact with input/output contacts of the various circuit elements on the integrated circuit chip being tested.
Chip contacts most often are the pads to be electrically connected to the next level of circuitry, and may be referred to as bond pads. Bond pads most often have an aluminum or copper surface, are rectangular in shape, and are recessed slightly below the surface of the passivation layer. Multiprobe testers and die carriers have a plurality of contact mechanisms attached to a substrate mirroring the chip bond pads, and the contacts are fanned to the perimeter by conductors.
A thin, but tenacious aluminum oxide, as well as other insulating contaminants exist on the surface of aluminum bond pads, requiring that the contaminants be penetrated in order to make good electrical contact for accurately testing the circuits. Similarly, copper is subject to various oxides, some of which are insulating and must be penetrated by the probe in order to be tested accurately.
FIG. 1 illustrates a probe card of known technology wherein a plurality of cantilevered needles 11 are arrayed and attached to conductive traces 12 on an insulating polymeric ring 10. The needles 11 are in contact with bond pads 14 on a wafer 15 which is supported on, and moved by a work station platform 13 of a tester.
The needles 11 or probe elements may be secured to the probe ring 10 by an adhesive, or they may be bonded, as by welding to a blade. Typically an opening is provided in the center of the ring for the needles to extend through, and for aligning the needles to bond pads on the device to be tested. The card is in contact with a probe head which provides electrical connection to the controlling computer, and which mechanically brings the needles into contact with bond pads on the chip.
FIG. 2 illustrates in more detail the shape of a conventional probe needle 21 of known art, typically made of rigid metal, such as tungsten. It can be seen from the shape of the needle, that as the tip is brought into contact with the horizontal surface of the IC 25, and as pressure is applied, the rigid tip will begin to penetrate the softer metal bond pad 24 surface. The work station 23 is then moved horizontally to effectively scrub the relatively soft metallic surface of the bond pads 24, and allow ohmic contact to be made.
The needles must be accurately positioned in order to assure that each one makes electrical contact with a contact location or bond pad on the integrated circuit. With conventional probe card needles, final positioning is accomplished by bending the needles after they are mounted on the probe card, which is laborious, time consuming, and expensive.
As the size of integrated circuit shrinks, it becomes more difficult to establish electrical contact with the chip bond pad metal because pads and the distance between pads has decreased, because needles and connections are too large, and because there is insufficient room to allow a scrubbing motion for the needles to penetrate the oxide. Therefore, testing some chips cannot be achieved with conventional needle contacts. In particular, testing with probe cards having conventional needle probes is nearly impossible for high density bond pads on ICs where the pad pitch is 75 microns or less, and the density of contacts is in the range of 400 or greater per device.
The tight pitch of probe needles, and the angles of their projection necessary for these devices is extremely difficult to manufacture, and in turn ensures a high cost. Further, both delivery and maintenance of such cards adds significantly to testing cycle time.
As a result of these issues, a number of attempts have been made to provide alternate probe card technology. Much of the newer technology centers around photolithographically defined conductor leads on polymeric membranes with plated or spring loaded contact mechanisms. Both die carriers and membrane probe cards usually rely on metallic balls or spheres as the contact mechanism. These approaches must have a means for scraping, and for applying pressure to cause the membrane to make uniform contact across the chip. Particulate matter, such as diamonds or metals have been incorporated in the contact devices in an attempt to break the bond pad surface insulators, but these are difficult to control, are subject to incorporation of contamination between the particles which interfere with contact, and further are expensive. The issue of uniform electrical contact, as well as alignment is further aggravated by thermal expansion of the membrane resulting from a significant amount of heat generated by the chip during the testing procedure.
Thin film conductors have an added risk of increased inductance to the circuit, which is a significant issue for testing high speed devices. On the other hand, high resistivity of some probe needles, conductor traces, and multiple connections between the needles, the conductors on the probe card, and those to the probe head can also lead to inductance values which adversely impact the accuracy of chip testing.
Membrane probe cards have a number of issues, including a high cost to fabricate. However, photolithography, etching, and plating does provide a means for conductor uniformity, and allow much more closely spaced conductors.
Because of the aforementioned issues with prior probe card technologies, and because of the anticipation of even tighter bond pad pitch on future integrated circuits, it would be very advantageous to the industry to have a reliable, low cost probe contact apparatus, having a rapid means of fabrication, modification, or repair, having low inductance, and a very high density of contacts.
It is an object of the current invention to provide a new and useful probe card and probe interface apparatus for establishing temporary electrical connection with high density integrated circuit chip input/output pads.
It is also an object of the invention to provide a reproducible method for rapidly and economically manufacturing a high density probe apparatus.
It is an object of the invention to provide multiple precisely dimensioned probe contact apparatus.
It is yet another object of the invention to provide a robust probe card contact apparatus which minimizes the amount of maintenance required during and after usage.
It is an object of the invention to provide a probe card contact apparatus which is compatible with existing probe card technology, and tester operation.
Yet another object of the current invention is to provide a reliable, high performance probe card contact apparatus capable of being compressed during contact, and returning to its original shape after contact pressure is removed for many testing cycles.
The objectives of this invention are met by providing a new xe2x80x9cmicroxe2x80x9d probe interface apparatus, hereafter referred to as xcexc-probe, and electrically and mechanically securing a plurality of xcexc-probes to precise locations on a substrate or probe card.
The xcexc-probe of the current invention includes a base and an angled probe tip which has been patterned and etched as a single unit from a thin sheet of conductive metal having high tensile and yield strength, and coated with highly conductive, noble metal. These material properties allow fabrication of very small, highly reliable contact devices capable of repeated use. The base of each xcexc-probe is inserted into a laser drilled slot in a probe card or other substrate, and is adhered to conductive traces on the substrate by soldering or conductive adhesive. Needle tips of the assembled probe card are brought into contact with a device under test (DUT) using conventional probe testing equipment and technology. When the angled probe tip is brought into contact with chip pads, it is partially compressed in the vertical direction, and as the DUT is moved in the horizontal direction, the pad surface is xe2x80x9cscrubbedxe2x80x9d to penetrate surface contaminants, and allow electrical contact to be made. When the probe card is raised, the spring-like xcexc-probe needle returns to its original shape.
Design of the xcexc-probe includes not only the base and probe tip, but also locking features, a stand-off to prevent over compression, and a necked down stem feature for release from the support strap used in transporting and plating during the manufacturing processes.
High resolution, rapid and low cost patterning of multiple xcexc-probes is accomplished using photolithographic patterning technology similar to that known from the printed circuit industry. The unprotected metal is etched by batch processing, and the parts are plated with a thin film of a highly conductive, noble metal.
The aforementioned probe interface apparatus, its design and method of manufacture is compatible with tight pitch, and high performance requirements of integrated circuits both in current production and those in plans for the future.
The foregoing and other objectives, features and advantages will become more apparent from the following detailed description of preferred embodiments of the invention which proceeds with reference to the accompanying drawings.